The present invention relates to flow separation detectors and, more particularly relates to feedback sensor arrangements adapted to provide for the measurement of surface aerodynamic flow phenomena, and especially with regard to aerodynamic flow separation which is encountered over a surface.
Currently, various types of detection or sensor systems are being investigated for their applicability to the technology concerning problems which are being encountered as a consequence of aerodynamic flow separation; for instance, such as during airflows over the wing surfaces of an aircraft, and which may have a important bearing on and potentially adversely influence the performance of the aircraft. For example, some of the systems being investigated provide for a so-called closed-loop control of aerodynamic flow separation, which necessitate the provision of feedback sensors which are sensitive to flow separation, and whereby such sensors are typically required to be surface-mounted on the surface or wall which is subject to aerodynamic flow separation. At this time, essentially fully developed and commercially available sensors employed for this purpose are pressure transducers which are capable of measuring surface aerodynamic phenomena and few separation parameters.
In particular, types of sensors which are adapted for the investigation or measurement of aerodynamic flow separation which takes place on a surface or wall may be so-called electronic xe2x80x9cthermal tuftxe2x80x9d sensors. Thus, in essence, thermal tuft sensors may be generally constituted of one or more electrical heating elements with temperature sensors being mounted spaced upstream and downstream thereof along the presumed directions of aerodynamic flows passing over a surface. Generally, the flow separation, encountered in at least a two-dimensional flow, is defined by a location wherein the flow proximate a wall over a surface tends to oppose a primary flow direction; pursuant to a phenomenon referred to as a backflow. Thus, the thermal tuft sensors are spacedly mounted in the presumed flow direction. The electrical heating elements are normally pulsed on and off, thereby heating a local packet of fluid providing the aerodynamic flow. Depending upon the local instantaneous direction of the flow, either the upstream or downstream located temperature sensor will detect a rise in temperature as the heated packet of fluid is convected therepast. Generally, the pulses are counted as a measure of the percentage of the time during which the flow is either upstream or downstream in its direction. Alternatively, the time internal between the heater element actuation and sensor detection can be recorded as a measure of near-wall upstream or downstream velocity magnitude.
Such electronic xe2x80x9cthermal tuftxe2x80x9d sensors are extensively described, in an article by Shivaprasad and Simpson entitled xe2x80x9cEvaluation of a Wall-Flow Direction Probe for Measurements in Separated Flowsxe2x80x9d, published in the Journal of Fluid Engineering, 1981. In that instance, a pair of thermal sensors are spaced along a surface whereby a free stream of a fluidic or airflow may have a flow direction extending across the locations of the sensors. A plurality of heaters are interposed between the sensors, and further heaters are arranged offset aside the directional flow so as to be able to determine aerodynamic separation or, in essence, a breakdown of a boundary-layer flow of fluid passing across the surface which may pass either directly across the sensors or at an angle relative thereto. These sensors are electronically connected to the electrical or electronic circuitry of a device which; for example, may be a part of an aircraft electrical operating system.
Although the foregoing thermal tuft sensors are generally satisfactory in operation in detecting flow separation phenomena, they require the input of electrical energy from the electrical components of various devices, or in connection with aircraft from the electrical aircraft system network, thereby representing a source for electrical energy drain and consumption.
Accordingly, in order to obviate or ameliorate the electrical energy requirements in the provision of feedback sensor arrangements, particularly such which are employed for a closed-loop control of aerodynamic flow separation; for instance, that on the wing of an aircraft wherein there can be encountered a breakdown of a boundary-layer flow which may adversely affect the performance of the aircraft, pursuant to the present invention, there has been developed a novel system of flow separation sensors which are based on fiber optics and which may be employed for separation feedback control. In particular, the sensors which are based on fiber optics may employ an optical tuft arrangement based on the thermal/fluidic principles of the electrical thermal tuft, but with the employing of fiber optics signal and energy transmission instead of electronics. To that effect, the light transmitted through the fiber optics is adapted to be converted into heat enabling a packet of heated fluid to be convected in the direction of a predominant aerodynamic flow, and to impact or contact one of the temperature sensors which are based on fiber optics at a small following time interval, so as to provide the required information concerning aerodynamic flow separation.
Although various sensors have been developed which are based on fiber optics, these are primarily employed for the measurement of strain, acceleration and temperature, and currently there is the development of new pressure transducers in the technology. However, none of these sensors in themselves are designed for flow separation detection, particularly for use in the closed-loop control of aerodynamic flow separation, or for investigations of breakdown phenomena in boundary layer flow situations.
Accordingly, it is an object of the present invention to provide an arrangement for the investigation of aerodynamic flow separation.
A more specific object of the present invention is to provide a sensor arrangement for the investigation of aerodynamic flow separation utilizing flow separation thermal tuft sensors which are based on fiber optics.
Yet another object of the present invention is to provide for novel feedback thermal tuft sensors which are based on fiber optics, wherein these are employed for aerodynamic separation feedback control, particularly with regard to aerodynamic flow separation taking place on the wing surfaces of an aircraft.
A still further more specific object of the present invention rises in the provision of feedback sensor arrangements for the closed-loop control of aerodynamic flow separation which are adapted to extend through or to be positioned within the skin structure of an aircraft wing or airfoil.